This invention relates to catalytic converter housings having a tubular central part and funnels connecting the central part to inlet and outlet pipes.
There are many different arrangements for catalytic converter housings which are used to mount a catalytic converter in the exhaust system of an internal combustion engine, especially for motor vehicles, and two arrangements have become established in the market. In the first arrangement, an expanded mat is wrapped around a monolith of ceramic or metallic design which is coated with a catalytically active material, the expanded mat being effective to support the monolith. A sheet-metal jacket is, in turn, placed on this expanded mat and is wound with a predetermined force, thereby holding the monolith in position. The tensioned sheet-metal jacket is tacked at its seam to form a tube so that the monolith is seated in a fixed manner. Inlet and outlet funnels are attached by circular welds at the ends of the tube and are aligned in accordance with the requirements for attachment to the exhaust pipe. After closing the tubular sheet-metal jacket by welding the seam, the finished wound converter is completed. Despite the high functional and process reliability of such wound converters, disadvantages have been found when they are used as standard fittings. One disadvantage is the high weight of the assembly and the other is that the funnels are often connected to the monolith surfaces in a way which interferes with the flow of exhaust gas through the monolith.
Another commercial arrangement for a catalytic converter housing, called the shell converter, avoids these disadvantages. In contrast to the wound converter, the shell converter consists of a monolith, an impregnated expanded mat, and two half-shells i.e., an upper half shell and a lower half shell. However, the shell converter has inadequate process reliability and, in addition, the geometry required by the shell form presents difficulties in fitting it to the undersurfaces of motor vehicles. Where there are variations in the shapes of the undersurfaces of motor vehicles, it is necessary to compensate for a difference in the exhaust pipe converter connection by a complex and thus costly pipe adaptation arrangement.
During the assembly of the shell converter, the expanded mat is dipped into an organic fluid to allow it to be installed more easily. This organic fluid subsequently evaporates, leaving the expanded mat very porous. Moreover, when the assembled converter is subjected to thermal loading, the converter shell expands to a very different extent than the monolith so that manufacture within very narrow tolerances is necessary for reliable functioning of the shell converter. If the narrow tolerances are not maintained, clearances open up, permitting movement of the monolith in the housing after the motor vehicle has been put into operation, and these can lead to failure of the catalytic converter. Such catalytic converter housing arrangements are known, for example, from German Patents Nos. 42 23 648, 38 21 397 and 38 11 224 and German Offenlegungsschrift No. 37 29 994.
A further difficulty in the assembly of the catalytic converter housing is encountered in the connection of a funnel to the tubular housing body. The funnel, which is provided to compensate for the differences in diameter between the inlet and outlet pipes and the tubular converter body, is intended, on the one hand, to ensure a controlled flow of exhaust gas and, on the other hand, to protect the expanded mat from being eroded by the pulsating flow of exhaust gas. For this purpose, the funnel collar is usually set at an angle of 90.degree. to the funnel axis, as shown, for example, in FIG. 5 of German Offenlegungsschrift No. 34 30 398.
Such funnels are usually produced from a sheet-metal blank by deep-drawing, but this results in two problems. On the one hand, the sheet-metal blanks have to be thick enough to provide sufficient thickness at the small end diameter after deep drawing to permit welding of the small end diameter to the exhaust pipe. The second problem origi nates from the 90.degree. positioning of the funnel opening relative to the funnel collar which is welded to the catalytic converter housing. In this case, depending on the position of the monolith diameter in its tolerance range within the tubular central part and any off-center fastening of the funnel collar to the catalytic converter housing, it may happen that an effective monolith area of up to 15% is covered by the funnel. An improvement in this regard is provided by the funnel connection shown in FIG. 1 of German Offenlegungsschrift 34 30 398, in which there is only a slight overlap of the funnel with the effective monolith end face. However, this connection requires high precision in the manufacture of the housing components and of the funnel since, otherwise, the funnel cannot be inserted into the housing with an accurate fit.
This becomes even more problematic because of the welding of three layers of sheet metal 1, 2, and 10 to the inlet funnel in the arrangement shown in FIG. 1 of German Offenlegungsschrift No. 3430398.
A further funnel connection is disclosed in German Offenlegungsschrift No. 34 30 399, in which the large diameter end of the funnel is folded over the catalytic converter housing. However, this is a very complicated process and does not remove the disadvantage of partial covering of the effective converter end face.